PRJ566 Project Planning
and Management
Lecture: Network Diagrams
To Create a Plan You Need…
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Work Breakdown Structure
Dependencies
Milestones
The Network
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Early/Late Start/End dates
Slack/Float
Critical Path
Task Dependencies
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Task A is said to be dependent on task B if
task B must precede task A (task B must be
finished before task A can start)
Task B is called a predecessor of task A
Task A can have many predecessors
Only “immediate predecessors” are referred
to as predecessors
Milestone
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A task with zero time allocated to it.
It is used as a “marker”; documentation.
It is not assigned to anyone.
Tasks can be dependent on milestones.
Network Diagram

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A pictorial representation of the sequence
in which the project work can be done
Shows the relationships (dependencies!)
between tasks
MS Project creates network diagrams for
you (=Gantt chart in MS Project)
Network Diagram
What order do I do these tasks in?
Network Diagram
1.1
Measure
Room
1.2
Choose
colors
4 Paint
Room
2
Purchase
Materials
1.3
Create
Materials
List
5.1 Clean
up
1.4
Create
Estimate
Sheet
5.2
Remove
Floor
Covers
4 Paint
Room
1.5
Review
with client
3.1 Move
Furniture
3.2 Wash
Walls
3.3 Cover
Floors
Network Diagram = Gantt Chart
1.1
1.3
1.4
1.5
1.2
2
4
3.1
3.2
3.3
5.1
5.2
Why are Network Diagrams
important?
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You can plan more effectively--you can
see the relationship between activities
Easier to reschedule--you can see impact
of changes
Allows you to monitor and control the
project--compare it against baseline
Calculating Slack/Float

What is the earliest/latest possible start of
each task?
Slack/Float time
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Free Slack: range in which task can finish
without causing delay in early schedule of
immediate successors
Total Slack: range in which task can finish
without causing delay to project
completion
Late and Early Start/Finish

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Early start/finish--earliest possible time
that a task can start/finish without causing
delay
Late start/finish--latest possible time that
a task can start/finish without causing
delay
Early Start/Finish
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ES = latest finish of
predecessors + 1
EF = (ES + duration) - 1
Early Start/Finish
2
1.2
1
1.1
3
2
2.1
1
1
6
5
2
1.3
2
1
2
1.4
2
5
1
8
6
2.2
4
3
1.5
7
6
1
6
2.3
6
1
2.4
9
2
Late Start/Finish
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LF = earliest start of successors - 1
LS = (LF - duration) + 1
Late Start/Finish
2
1.2
3
2
3
1
1.1
4
5
2
1.3
1
2.1
1
1
1
6
2
1.5
4
3
6
8
2.4
2
7
8
6
7
9
1
5
2.3
4
7
7
5
2
6
2.2
4
2
2
6
1
1
4
1.4
5
7
6
1
7
9
Slack/Float time
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The delay (in units of time) that could be
tolerated in starting or completion time of a
task without causing a delay in the project.
Slack time for a task = LF - EF
Slack Time = LF - EF
2
1.2
3
1
2
1
4
5
2
1
1.3
0
1
6
2.1
1
1.1
1
3
4
2
1
2
1.5
0
4
1.4
4
3
7
7
6
1
1
8
2.4
6
7
6
1
1
7
9
2
0
7
8
2.3
4
0
5
0
2
2
6
1
2.2
5
2
5
6
7
9
Critical Path
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Longest duration path in network
diagram
Sequence of tasks whose early and late
dates are the same
Sequence of tasks with zero slack
Critical Path
2
1.2
3
1
2
1
4
5
2
1
1.3
0
1
6
2.1
1
1.1
1
3
4
2
1
2
1.5
0
4
1.4
4
3
7
7
6
1
1
8
2.4
6
7
6
1
1
7
9
2
0
7
8
2.3
4
0
5
0
2
2
6
1
2.2
5
2
5
6
7
9
Why care about Critical Path?
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Tasks on this path need to be on time!
If you know what they are you can track
them!
Critical Path
1.1
1
2.4
2
1.2
2
1.3
1
1.4
3
3.1
1
1.5
3.2
1
2
4
2.1
2
2.2
1
2.3
1
2
2.4
2
Critical Path
Dependencies with Lag Time
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Lag time is time that must elapse after one
task is completed before the dependent task
can start
How do we show this in MSProject?
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Use the lag time variable in the task definition
These tasks fit all criteria
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Longest duration path in network diagram
Sequence of tasks whose early and late
dates are the same
Sequence of tasks with zero slack
Why care about Critical Path?

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Tasks on this path need to be on time!
If you know what they are you can track
them!
You can compress, adjust for maximum
benefit
Management Reserve
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A contingency Budget of time--a time bank
5 to 10 % of total duration
Withdraw from it when you run into
trouble
Monitor it to see how much you’re using it
(overuse means trouble!)